pub unsafe trait CloneFromCell: Clone { }🔬This is a nightly-only experimental API. (
cell_get_cloned #145329)Expand description
Types for which cloning Cell<Self> is sound.
§Safety
Implementing this trait for a type is sound if and only if the following code is sound for T = that type.
#![feature(cell_get_cloned)]
fn clone_from_cell<T: CloneFromCell>(cell: &Cell<T>) -> T {
unsafe { T::clone(&*cell.as_ptr()) }
}Importantly, you can’t just implement CloneFromCell for any arbitrary Copy type, e.g. the
following is unsound:
#![feature(cell_get_cloned)]
#[derive(Copy, Debug)]
pub struct Bad<'a>(Option<&'a Cell<Bad<'a>>>, u8);
impl Clone for Bad<'_> {
fn clone(&self) -> Self {
let a: &u8 = &self.1;
// when self.0 points to self, we write to self.1 while we have a live `&u8` pointing to
// it -- this is UB
self.0.unwrap().set(Self(None, 1));
dbg!((a, self));
Self(None, 0)
}
}
// this is not sound
// unsafe impl CloneFromCell for Bad<'_> {}Dyn Compatibility§
This trait is not dyn compatible.
In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.
Implementors§
impl<A: CloneFromCell, Z: CloneFromCell, Y: CloneFromCell, X: CloneFromCell, W: CloneFromCell, V: CloneFromCell, U: CloneFromCell, T: CloneFromCell> CloneFromCell for (A, Z, Y, X, W, V, U, T)
impl<B: CloneFromCell, A: CloneFromCell, Z: CloneFromCell, Y: CloneFromCell, X: CloneFromCell, W: CloneFromCell, V: CloneFromCell, U: CloneFromCell, T: CloneFromCell> CloneFromCell for (B, A, Z, Y, X, W, V, U, T)
impl<C: CloneFromCell, B: CloneFromCell, A: CloneFromCell, Z: CloneFromCell, Y: CloneFromCell, X: CloneFromCell, W: CloneFromCell, V: CloneFromCell, U: CloneFromCell, T: CloneFromCell> CloneFromCell for (C, B, A, Z, Y, X, W, V, U, T)
impl<D: CloneFromCell, C: CloneFromCell, B: CloneFromCell, A: CloneFromCell, Z: CloneFromCell, Y: CloneFromCell, X: CloneFromCell, W: CloneFromCell, V: CloneFromCell, U: CloneFromCell, T: CloneFromCell> CloneFromCell for (D, C, B, A, Z, Y, X, W, V, U, T)
impl<E: CloneFromCell, D: CloneFromCell, C: CloneFromCell, B: CloneFromCell, A: CloneFromCell, Z: CloneFromCell, Y: CloneFromCell, X: CloneFromCell, W: CloneFromCell, V: CloneFromCell, U: CloneFromCell, T: CloneFromCell> CloneFromCell for (E, D, C, B, A, Z, Y, X, W, V, U, T)
impl<T: CloneFromCell> CloneFromCell for Option<T>
impl<T: CloneFromCell> CloneFromCell for (T₁, T₂, …, Tₙ)
This trait is implemented for tuples up to twelve items long.